The present invention relates to an air separation plant, more specifically to an air separation plant which separates oxygen, nitrogen, argon, etc. as products by cooling, liquefying and distilling air and which utilizes effectively the damping effect of a powdery thermal insulator packed in it under atmospheric pressure for each equipment in the plant.
Conventionally, air separation plants are aseismatically designed based on the Aseismatic Design Standard for High-pressure Gas Equipment (Japan) etc. Such aseismatic designs are as described below.
Housings (cold boxes) and free-standing columns and/or tanks and/or the like are aseismatically designed respectively. First, each equipment is modeled by some mass points and springs for seismic analysis. Next, a horizontal design basis earthquake predetermined according to the degree of importance of a content in the plant housing, the area where the plant is installed and the ground classification is acted upon the seismic model to analyze responses of the plant to the earthquake. As a method of this response analysis, there are employed the seismic coefficient method for housings having natural periods of not higher than the values predetermined according to the ground classification and for columns and/or tanks, and the like, (including, for example, heat exchangers and/or condensers and/or reboilers, and they are all hereinafter generally referred simply to as "columns") having degrees of importance belonging to II or III (i.e. the degree of importance of the Aseismatic Design Construction regulated by the Aseismatic Design Standards for High-Pressure Gas Equipment which is based on Japanese General High-Pressure Gas Safety Regulations) and having heights of lower than 20 m measured from base plates; the modified seismic coefficient method for columns having heights of 20 m or higher and natural periods of not higher than the values predetermined according to the ground classification; and the modal response analysis method for columns and housings having natural periods of higher than the predetermined values.
Then, an estimated stress for aseismatic design, which is expressed by the sum of the earthquake loads occurring at each part (corresponding to the location of each mass point in the seismic model) of an equipment determined by the response analysis and loads caused by the internal pressure, the dead load, etc. which are applied to each part during steady operation of the plant, is calculated using a defining equation. Design specifications for each equipment are decided such that the estimated stress values at the respective parts may not exceed allowable stress values respectively. In making this decision, the mass of a thermal insulator packed in the housing is considered, but its stiffness is not considered.
Further, for those columns which are to be mounted on frames, the design modified earthquake, which is determined depending on the ratio of the natural frequency of the columns to that of the frame therefor, is used to carry out response analysis according to the seismic coefficient method. In this case, the frames are of rigid. Estimated stress values for aseismatic design are also calculated to work out aseismatic designs for them such that they may have stress values not greater than the allowable stress values. In this case again, the mass of the thermal insulator is taken into consideration but its stiffness is not, like in the case of the free-standing columns etc.
Meanwhile, the present inventors found that even a powdery thermal insulator packed under atmospheric pressure into the housing and between columns and/or tanks and the like shows coupling to influence the vibration characteristics of the housing and the columns, particularly of free-standing columns. It was found, for example, that the thermal insulator shows coupling as the housing and columns vibrate to increase in some cases responses of free-standing columns depending on the correlation between the natural frequency of the housing and that of the free-standing columns.